Radio receiving apparatus



Nov. 14, 1933. J. M. MILLER 1,934,940

RADIO RECEIVING APPARATUS Filed Nov. 8, 1929 INVEN2 R BY 1. 2114; mm

{k ATTORNEY Patented Nov. 14, 1933 UNITED. STATES PATENT OFFICE RADIO RECEIVING APPARATUS Application November 8, 1929. Serial No. 405,575

11 Claims.

My invention relates to the control of volume of reproduction of radio receiving apparatus comprising tuned radio frequency amplifiers utilizing thermionic tubes, and more particularly to either or both the transfer to and amplification of signal energy by an amplifier of that type.

In accordance with my invention, to permit the reception of strong signals at suitably reduced volume and without distortion, there are provided suitable instrumentalities for varying both the transfer of signal energy as from an antenna system to the amplifier, and the amplification characteristic of one or more amplifier tubes of the screen grid type, and more specifically, and particularly to avoid marring of reception by tube noises, the controls are so related that to reduce volume the amplification characteristic of the tubes is at first lessened rapidly with little or no change of effective input energy, and thereafter the transfer of energy to the amplifier is progressively and more rapidly reduced; preferably, amplification is controlled by varying the screen-grid potential, it being provided however that this potential can not be adjusted to any value below a predetermined minimum to preclude the occurrence of distortion during the control of volume of strong signals.

In another aspect of my invention and particularly in the system described, the antenna system or circuit includes a resistance adjustable to vary the transfer of signal energy to the amplifier and is coupled or connected to the first tuned circuit by a condenser of small capacity to minimize the detuning effect of the antenna or variation thereof and to insure that the damping effect upon the tuned circuit by the volume control resistance is of negligibly small magnitude for all adjustments thereof.

My invention further resides in the method, system, and features hereinafter described and claimed.

Reference is to be had to the accompanying drawing in which there is diagrammatically represented radio receiving apparatus utilizing my invention.

Signal energy absorbed by the antenna A is transferred through condenser K to the tuned circuit L1 C1 in the input system of the tube V1 in whose output system is disposed a second tunable circuit L2 C2 comprising the tunable input system of a second amplifying tube V2 whose output system comprises a third tunable circuit L3 C3 which may be as indicated included between the input electrodes of a detector tube D. If desired the rectified signal energy may be amplified at audio frequencies by suitable and known apparatus not shown. A suitable translating device, as an electrodynamic speaker, reproduces the signal, for example music, speech,

or the like.

The radio frequency amplifier tubes V1, V2, are preferably, and as shown, of the screen grid type having a shielding electrode g1 between the anode a and the control grid g. The potential of the screen grids 91 is derived from a potentiometer resistance P connected across the output terminals of the filter system comprising the inductances Z1, Z2 and the capacities K4, K5 and K6 which filter is fed by transformer T and double wave rectifier V3. The field winding F of a dynamic speaker is connected between the points 1, 2 in the negative lead 3 of the filter in which case the field winding additionally functions as a filter choke. The secondary hl of the transformer T furnishes current to the heaters 71. of the tubes V1, V2 and D.

Movement of the contact S along the potentiometer resistance P varies the potential of the screen grids g1 of tubes V1 and V2 and therefore the amplifying power or characteristic of the tubes. When the received signals are of great amplitude as from a nearby or powerful station, control of volume solely by adjustment of contact S is not satisfactory as it is necessary to reduce the potential of the screen grids 91 to such low value that the tubes V1, V2 do not function in a normal manner. When the screen grid potential is unduly low and strong signals are being received, distortion in the radio frequency known as breaking through and interference called cross-talk are experienced.

To prevent this interference and distortion, the lowest value to which the screen grid potential may possibly be adjusted is maintained suitably high, as for example, 20 volts for W 224 tubes, although this voltage may vary depending upon other factors, as plate voltage etc. In the example shown, the amplification control resistance R1 is an intermediate section of the potentiometer P between the positive terminal thereof and a connection 5 therefrom to the cathodes c of the tubes. The drop of potential across the portion R2 of the potentiometer resistance betwen the conductor 5 and the lower end of resistance R1 is suitably great to insure normal operation of the screen grid tubes for all positions to which the contact S is adjustable, including its lowest position. It will be understood that resistance R1 is preferably physically separate from other portions 91 potentiometer resistance P.

- crement of movement.

While I have shown the screen-grid potential derived from a potentiometer resistance, and the minimum potential determined by the magnitude of a fixed resistance, it will be understood that the biasing potential may be otherwise derived and its minimum value otherwise determined without departing from the spirit of my invention.

To permit satisfactory reception from powerful or nearby stations, there is additionally employed an arrangement for varying the transfer of energy to, from, or between the amplifier circuits. Preferably, and as shown; a resistance R is included in the absorptionclrcuit between the antenna A and the earth E, adjustment of the movable contact S1 varying the effective magnitude of the resistance in shunt to the first tunable circuit Ll, C1. Control of volume solely by the resistance R is not satisfactory since to receive signals from nearby or powerful stations at suitably low intensity the contact S1 must be moved adjacent the upper or antenna terminal of the resistance R1. The amplification being high, there is excessive disturbance due to tube noises etc.

In the reception of strong signals, it is desirable both to reduce the amplifying power of the tubes and of the energy transferred. Preferably, and as shown, the contacts S and S1 for controlling amplification and signal transfer respectively, are mechanically connected for simultaneous movement by a control knob Vc.

It will be understood that in the arrangement shown in the figure the slider S1 is moved upwardly and slider S moved downwardly to reduce volume and vice versa. Starting from the position of maximum volume, 1. e. with slider S1 in its extreme lower position and slider S in its extreme upper position, the amplification is at first rapidly reduced by movement of slider S with only slight effect upon signal transfer by movement of slider S1. As movement of the slider contacts is continued the signal transfer is reduced at a more rapid rate which is very high as slider Sl closely approaches its extreme upper position. The mechanical connection between the sliders efiecting their simultaneous movement in predetermined relation to each other insures that for all positions of the volume control adjusting element or knob Vc, the ratio of signal to tube noises is high. For each position of the volume control knob, proportionate amounts of control efiected by change in amplification and of energy transfer respectively may be predetermined by suitably constructing or designing the resistances, or less preferably by effecting change in the relative position of the contact slider S, S1 with respect to each other. For example, to enhance the signal-noise ratio, the resistances may be so wound and their sliders so mechanically connected that when one slider is cooperating with its resistance to effect a large percentage change in resistance for an increment of movement, the other slider effects small percentage change for a like in- In copendingv Macnabb applicationSerial No. 476,013, there is disclosed and broadly claimed generally similar but specifically different methods and apparatus.

The condenser K is in series with the resistance R in a path in shunt to the first tuned circuit L1, C1. The resistance of the resistor R may be of the order of 10,000 ohms and the capacity of condenser K of the order of 10 micro-microfarads.

To reduce damping, the natural capacity A1 of the open antenna system is directly in shunt t0 the portion of the resistance R between the slider s1 and the antenna A and is an effective bypass except as the resistance R approaches a low value, comparable to or less than the reactance of the antenna capacity, under which circumstance its damping effect upon tuned circuit L1,. 01 is small. Furthermore this condition would obtain only in the reception of a very strong signal in which case damping and the consequent loss of selectivity would be 01' no importance.

The coupling or connection of the antenna circuit to the first tuned circuit Ll, C1-through the condenser K of small capacity mnimizes the detuning effect of the antenna and permits the condensers C1, C2 and C3 to be mechanically coupled for movement in unison.

In circuit between the anodes a of the tubes V1 and V2 and the positive terminal of the filter network, there are included the radio frequency choke coils L4 between the anode ends of which and a suitable point of the inductances L2 and L3 there are connected the condensers K1, K1 effective to prevent passage of direct current through the input inductance to ground. The condensers are preferably connected to a point midway between the ends of the inductances to reduce the effect upon the tuning of the capacity of the anode to ground which in the case of screen grid tubes is relatively large. The coils or autotransformers L1, L2, L3- are preferably of Litzendraht and are bank wound.

Insofar as the dual control aspect of my inven tion is concerned, the amplification may be controlled by varying the biasing potential applied to the control grid structure of one or more screengrid tubes, it being understood, however, that in adjusting from maximum to minimum volume the amplification is at first rapidly reduced with little or no effect by change of signal transfer and as minimum volume is approached the greater part of the volume change is effected by change of signal energy transfer with little or no variation of amplification. This staggering results in quiet operation of the control with no impairment of the quality of reproduction.

What I claim is:

1. In the operation of an amplifier utilizing screen grid tubes, the method of reducing volume which comprises reducing the positive screen grid biasing potential of one or more of said tubes to effect substantial decrease of volume by reduction of amplification and simultaneously lessening the signal energy transferred to effect relatively small decrease of volume, and thereafter to effect further reduction of volume, lessening the transfer of signal energy to cause relatively great decrease of volume and simultaneously reducing the amplification with little or no effect upon the volume of signals.

2. In the operation of radio receiving apparatus utilizing screen grid tubes, the method of reducing the volume of reproduced signals which comprises simultaneously decreasing the positive screen grid biasing potential of by one or more of said tubes to decrease the amplification of the signal energy at radio frequency and the transfer .of signal energy at radio frequency, the reduction plied to one of the grid structures of one or more of said tubes amplifying the signal energy at radio frequency and decreasing the transfer of signal energy at radio frequency, the reduction at first being preponderantly by decrease of amplification and subsequently preponderantly by decrease of transferred signal energy.

4. In theoperation of radio receiving apparatus utilizing screen-grid tubes, the method of varying the volume of reproduced signals which comprises simultaneously varying the screen-grid potential of one or more of said tubes amplifying the signal energy .at radio frequency and the transfer of radio frequency signal energy cumulatively to change the amplitude of reproduction, the reduction from maximum volume at first being effected preponderantly by change of amplification and further reduction preponderantly by change of signal energy transfer.

5. In the operation of radio receiving apparatus utilizing screen grid tubes, the method of reducing the volume of reproduced signals which comprises simultaneously varying the biasing potential applied to the grid structure of one or more of said tubes amplifying the signal energy at radio frequency and decreasing the transfer of signal energy at radio frequency, the reduction at first being preponderantly by decrease of amplification and subsequently preponderantly by decrease of transferred signal energy, and limiting the grid-biasing potential at minimum volume to a value at which distortion is negligibly small or absent.

6. In the operation of an amplifier utilizing one or more screen-grid tubes, the method of controlling the volume of reproduced signals which comprises varying the screen-grid potential inversely to the magnitude of the signal energy, limiting the minimum screen-grid potential to a value suitably h'gh to prevent distortion, and varying the transfer of unamplified signal energy to the amplifier, the control of volume by change of screen grid potential being within limits for which there is insubstantal distortion, and by transfer of signal energy within limits for which high ratio of signal to noise obtains.

7. In the operation of an ampl fier utilizing one or more screen-grid tubes, the method of controlling the volume of reproduced signals which comprises simultaneously varying the magnitude of signal energy transferred and the screen-grid potential, and limit'ng the minimum screen-grid potential to a value suitably high to prevent distortion, the reduction from maximum volume being at first preponderantly by decrease of positive screen grid basing potential, and subsequently preponderantly by decrease of transfer of signal energy.

8. In radio receiving apparatus comprising one or more cascaded tunable circuits and thermionic tubes, the method which comprises transferring received energy from an antenna to the first of said tunable circuits through a small capacity, controlling the magnitude of transferred energy by varying the resistance of a path in shunt to the antenna capacity, and simultaneously with said variat'on of energy varying the amplifying characteristic of one or more of said tubes to change the volume of reproduction, reduction from maximum volume at first being preponderantly by decrease of amplification and subsequently preponderantly by decrease of signal transfer.

9. Radio receiving apparatus utilizing screen grid tubes, means for changin the screen grid biasing potential to vary the amplification of one or more of said tubes, means to vary the transfer of signal energy, and structure mechanically coupling said means to effect simultaneous operation, said means and structure being of such nature and so related that from maximum volume adjustment of said structure effects change of volume principally by change of amplification and subsequently effects change of volume principally by change of signal energy transfer.

10. Radio receiving apparatus utilizing screen grid amplifier tubes, a continuously adjustable resistance for varying the'screen grid potential to control the amplification of received signals, means limiting the minimum screen grid potential, a resistance adjustable to vary the input energy of the amplifier, and structure mechanically coupling the adjusting elements of said resistances for simultaneous operation in controlling volume, the movement of said structure in one part of its range effecting change in volume preponderantly by change of screen grid potential, and in another part of its range effecting change in volume preponderantly by change of input energy to the amplifier.

11. In combination with radio receiving apparatus comprising one or more tunable circuits, and one or more screen grid tubes, an adjustable resistance of suitably high magnitude adapted to be included in an antenna circuit, a path in shunt to the first of said tunable circuits including the effective portion of said resistance and a reactance of suitably high magnitude, a second resistance adjustable to vary the screen grid potential, and structure mechanically coupling said resistances for adjustment in unison in controlling volume, the movement of said structure in one part of its range effecting change in volume preponderantly by change of screen grid potential, and in another part of its range eifecting change in volume by change of energy transfer to said first tunable circuit.

JOHN M. MILLER. 

